1. Field of the invention
This invention relates to an apparatus for effecting sealed separation of a two-phase fluid within a single container, and more specifically to the separation of blood serum or plasma from the blood cells.
2. Prior art
The U.S. Pat. No. 3,508,653, granted to Charles M. Coleman on Apr. 28, 1970, describes a container assembly for effecting sealed separation of blood into a light phase and a heavy phase. The disclosed assembly comprises a rigid tubular container adapted to receive a blood sample and housing a resilient piston in sealing contact therewith. The piston is adapted to be moved downwardly through the light phase, responsive to an applied force, while permitting upward flow of the light phase therearound. When the piston reaches the sealing region, the applied force is withdrawn, and the piston establishes a seal with the internal surface of the tubular container.
One problem inherent with the apparatus described in the patent to Coleman is that if the piston is designed so as to permit a satisfactory upward flow of the light phase therearound, then there is a hazard that the permanent seal of the piston with the internal surface of the tubular container at the sealing region is unsatisfactory. Another hazard inherent in a piston design so as to permit a satisfactory upward flow of the light phase therearound is that fibrin threads and crushed blood cells may be drawn with the light phase, past the piston, and cause problems or errors at the analysis.
Another apparatus for effecting separation of blood into a light phase and a heavy phase is described in U.S. Pat. No. 3,512,940, granted on May 19, 1970, to Justine J. Shapiro. The apparatus described in the patent to Shapiro comprises a hollow plunger acting as a piston. The plunger has a porous bottom portion serving as a filter.
One important drawback of filters of this and similar types is that although they may be able to adequately separate the light blood phase from the heavy phase, they are never able to completely prevent contamination of the serum or plasma by various constituents of the heavier phase, as time passes by.
Further, in many cases, the filter constitutes a separate body which forms a part of the piston, and, thus, the filter has to be inserted into the piston or attached thereto by a separate, time consuming and expensive step.